The endovascular treatment of a variety of vascular maladies throughout the body is an increasingly more important form of therapy. Catheters have been used to place various treatment materials, devices, and drugs within arteries and veins in the human body. Examples of these devices and their use in such treatments are shown in U.S. patent application Ser. No. 07/806,898 ("Detachable Pusher-Vasoocclusive Coil Assembly with Threaded Coupling") and Ser. No. 07/806,912 ("Detachable Pusher-Vasoocclusive Coil Assembly with Interlocking Ball and Keyway Coupling"). These show methods and devices for delivery of coils or wires within the human body to sites such as aneurysms, to occlude those sites. Coils such as are discussed in U.S. Pat. No. 4,994,069, may be of a regular or helical configuration or assume a random convoluted configuration at the selected site. The coils normally are made of a radiopaque, biocompatible metal such as platinum, gold, tungsten, or alloys of these and other metals.
In treating aneurysms it is common to place a number of coils within the aneurysm. The coils occlude the site by posing a physical barrier to blood flow and by promoting thrombus formation at the site.
Coils have typically been placed at the desired site within the vasculature using a catheter and a pusher. The site is first accessed by the distal end of a catheter. In treating peripheral or neural conditions requiring occlusion, the sites are accessed with flexible, small diameter catheters such as those shown in U.S. Pat. Nos. 4,739,768 and 4,813,934. The catheter may be guided to the site through the use of guidewires (see U.S. Pat. No. 4,884,579) or by flow-directed means such as balloons placed at the distal end of the catheter. Use of guidewires involves the placement of relatively long, torqueable proximal wire sections within the catheter, which proximal sections are attached to more flexible distal end wire section designed to be advanced across sharp bends at vessel junctions. The guidewire is visible using x-ray and allows a catheter to be manipulated through extremely tortuous vessels, even when such vessels are surrounded by soft tissue such as the brain.
Once the selected site has been reached, the catheter lumen is cleared by removing the guidewire (if a guidewire has been used), and the coil is placed into the proximal open end of the catheter and advanced through the catheter with a pusher. Pushers are wires having a distal end that is adapted to engage and push the coil through the catheter lumen as the pusher is advanced through the catheter. When the coil reaches the distal end of the catheter, it is discharged from the catheter by the pusher into the vascular site. This technique of discharging the coil from the distal end of the catheter has a number of undesirable limitations. First, because of the plunging action of the pusher and the coil, the positioning of the coil at the site cannot be controlled to a fine degree of accuracy. Second, once the coil has left the catheter, it is difficult to reposition or retrieve the coil if such is desired. Nevertheless, the technique has the benefit of delivering multiple coils at low cost with a short delivery time.
Several techniques have been developed to enable more accurate placement of coils within a vessel. In one technique (U.S. Pat. No. 5,122,136, issued Jun. 16, 1992) the coil is bonded via a metal-to-metal joint to the distal end of the pusher. The pusher and coil are made of dissimilar metals. The coil-carrying pusher is advanced through the catheter to the site and a low electrical current is passed through the pusher-coil assembly. The current causes the joint between the pusher and the coil to be severed via electrolysis. The pusher may then be retracted leaving the detached coil at an exact position within the vessel. In addition to enabling more accurate coil placement, the electric current may facilitate thrombus formation at the coil site. The only perceived disadvantage of this method is that the electrolytic release of the coil requires a period of time so that rapid detachment of the coil from the pusher does not occur.
Another technique for detaching an embolic coil shown in U.S. patent application No. 07/806,912. In that document, a coil having an enlarged portion is mated with a pusher having a keyway adapted to receive the enlarged portion of the coil in an interlocking relationship is covered by a coaxial member about the pusher and the coil. The coaxial member is movable by sliding the member axially. As the coaxial member is moved away from the junction where the coil's member engages the member of the keyway of the pusher, the coil disengages and the pusher is removed.
Another device for placement of coils is shown in U.S. patent application No. 07/806,898. This device includes a coil having a helical portion at one end and a pusher which is threaded to the inside of the helical coil by the use of a threaded section on the outside of the pusher. The device operates to release the coil by engaging the proximal end of the coil with a sleeve while the pusher is unthreaded. Once the pusher is free, the sleeve may be used to push the coil out into the treatment area.
Another method of placing an embolic coil is shown in U.S. Pat. No. 5,108,407. This patent shows the use of a device in which embolic coils are separated from the distal end of a catheter by the use of heat-releasable adhesive bonds. The coil adheres to the therapeutic device via a mounting connection using a heat sensitive adhesive. Laser energy is transferred through a fiber optic cable, which cable terminates at the connector. The connector becomes warm and releases the adhesive bond between the connector and the coil.
None of these disclosed devices suggest coils having interlocking ends which allow an embolic coil to be positioned within a vessel and then released upon ejection of the coil from the catheter distal end or, optionally, upon retraction of a control wire positioned within that interlocking end.